1. Field of the Invention
The present invention relates to semiconductor processing technology and, in particular, concerns a device and a fabrication process, whereby a Magnetoresistive Random Access Memory (MRAM) structure can be formed.
2. Description of the Related Art
MRAM is a developing technology that offers the advantages of non-volatile memory with high-density fabrication. An MRAM structure employs the properties of layered magneto-resistive materials, which utilize the spin characteristics of electrons to produce a selective resistance differential across the MRAM structure. Changes in the spin characteristics of magneto-resistive materials result in changes in the resistance of the MRAM structure, and changes in resistance may be sensed thereby permitting the use of layered magneto-resistive materials in logic state devices.
MRAM devices typically include a pinned (spin stationary) layer, a soft (spin programmable) layer, and a non-magnetic layer interposed therebetween. The soft or sense layer may be programmed through the application of an external magnetic field and the net magnetization vectors between the programmable layer and the pinned layer may be changed between two discrete quantities, which may then be sensed to detect the programmed logic state of the MRAM device.
MRAM devices follow the same high-density fabrication techniques as their semiconductor counterparts. Integrated circuit (IC) fabrication techniques employ sequential steps of layered processing of materials. In one aspect, current manufacturing processes utilize a flow process that deposits a layered magnetic stack structure onto a substrate, where the deposition of the layered magnetic stack structure includes the deposition of the magnetic pinned layer, the non-magnetic layer, and the magnetic sense layer onto the substrate. Once the magnetic stack structure is deposited, the magnetic pinned layer is defined with a photo patterning and dry or wet etching process in a manner known in the art. The last step in the flow process planarizes the magnetic stack structure to define a plurality of magnetic bit shapes using a dry or wet etching process, and then a top electrode is added to complete the MRAM memory structure.
One disadvantage to utilizing a selective wet etching process and/or a dry etching process to define the magnetic bit shapes and/or the magnetic stack structure is that it leaves substantially rough edges, which may reduce the switching reliability of the MRAM device. In addition, another disadvantage is that utilizing a selective wet etching and/or a dry etching process may undercut the barrier layer, which undermines the integrity of the barrier layer and may cause electrical shorting of the magnetic sense layer and/or the magnetic pinned layer. The electrical shorting effect may also contribute to unreliable switching of the MRAM device due to an uncontrolled leakage current.
Still another disadvantage to a selective wet etching and/or a dry etching process is the generation of a non-uniform magnetic bit shape. A non-uniform magnetic bit shape may adversely effect the magnetic coupling and the resistance of the magnetic stack structure. Unfortunately, irregular shapes and non-uniform structures may produce unpredictable magnetic coupling patterns that may require a larger magnetic field for switching. An adverse increase in the magnetic coupling effect of the magnetic stack structure may require a larger magnetic field for switching, which may result in a larger current draw through the MRAM device. Additionally, increased resistance through the magnetic stack structure may also require a larger current draw through the MRAM device. As a result, an increase in the current consumption of the MRAM device reduces the power efficiency of the MRAM device, which is disadvantageous to low power requirements of some electronic devices, such as laptop computers and cellular phones.
Based on the foregoing, there currently exists a need for an improved magnetic memory device that comprises magnetic memory stack layers with improved magnetic coupling characteristics and stability. Furthermore, there also exists a need for a magnetic memory fabrication process that reduces the use of a selective wet etching process or a dry etching process to define the magnetic bit shapes and/or the magnetic stack structure in a manner so as to improve the switching reliability of the magnetic memory device.